Seems to me it makes more sense in theory for layering purpose to use 2 pairs vs a thick single baselayer.A couple of questions:should you use a mid and a lightweight pair or 2 lightweights?Second, if you normally wear a medium would your 2nd pair be a medium or large so it aint too tight?Medium fits me snug-tight whereas large is baggy on me so if my 2nd layer was baggy in areas i guess this would defeat the purpose?

The less layers you have to bind, the better off you'd be
on 12/31/2012 13:55:20 MST

that being said, a silk-weight layer or comparable under an another base layer isn't going to be much of an issue. What are you wearing for pants, and how cold will it be when you are snow shoeing? I wear woven softshell pants and couldn’t imagine wearing a heavy base layer or a mid/light weight layer combination and not be too warm. I’d much rather be cool when active than hot. As with the others above in winter with a light weight base and softshell pants I layer insulation over the top for real warmth when needed. I am not taking my pants off (maybe for multiple days on an overnight trip) to adjust my base layer.

If the temperature is fluctuating a lot, then you need the maximum versatility in layers. That probably means thin layers with a thicker layer over. That way, you can wear zero, one, or two thin layers.

For one high-altitude expedition, we knew that it was going to be pretty consistently cold, so I wore medium weight fleece tights with thick wool trousers over that. That went for a couple of weeks, and for most days I had goretex rain/wind pants on over that.